How to Use Regex in Python: Simple Guide with Examples

In Python, you use regex by importing the re module and applying functions like re.search(), re.match(), or re.findall() with a pattern string. Regex patterns let you find, match, or replace text based on rules you define.

Syntax

To use regex in Python, first import the re module. Then use functions like re.search(pattern, string) to find a pattern anywhere in the string, re.match(pattern, string) to check if the string starts with the pattern, or re.findall(pattern, string) to get all matches.

The pattern is a string that defines the regex rules, and string is the text you want to search.

python

import re

pattern = r"\d+"  # matches one or more digits
text = "There are 12 apples and 30 bananas."

match = re.search(pattern, text)
if match:
    print("Found:", match.group())

Output

Found: 12

Example

This example shows how to find all numbers in a text using re.findall(). It prints each number found.

python

import re

text = "My phone numbers are 123-456-7890 and 987-654-3210."
pattern = r"\d{3}-\d{3}-\d{4}"
numbers = re.findall(pattern, text)

for number in numbers:
    print(number)

Output

123-456-7890
987-654-3210

Common Pitfalls

• Forgetting to use raw strings (prefix r) for regex patterns can cause errors because backslashes are treated as escape characters.
• Using re.match() when you want to find a pattern anywhere in the string instead of only at the start.
• Not checking if a match was found before calling .group(), which causes errors.

python

import re

text = "Hello 123"
pattern = "\\d+"  # Without raw string, backslash must be doubled

# Wrong: no raw string, might cause confusion
match = re.search(pattern, text)
if match:
    print("Found:", match.group())

# Correct: use raw string for pattern
pattern = r"\d+"
match = re.search(pattern, text)
if match:
    print("Found:", match.group())

Output

Found: 123
Found: 123

Quick Reference

Here are some common regex functions and their uses in Python:

Function	Purpose
re.search(pattern, string)	Finds first match anywhere in string
re.match(pattern, string)	Checks if string starts with pattern
re.findall(pattern, string)	Returns all matches as a list
re.sub(pattern, repl, string)	Replaces matches with repl
re.compile(pattern)	Prepares regex pattern for reuse

Key Takeaways

Always import the re module to use regex in Python.

Use raw strings (r"pattern") to write regex patterns safely.

Use re.search() to find a pattern anywhere, re.match() only at start.

Check if a match exists before accessing match.group() to avoid errors.

re.findall() returns all matches as a list for easy processing.